The number of global and regional satellite communication and navigation systems has grown rapidly in recent years among military, civil and commercial users around the world. In general, satellite-based communication and navigation systems provide location and time information. Typically, satellite communication and navigation systems may function anywhere on or near the Earth where there is an unobstructed line of sight to one or more satellite. Thus, satellite signals may not be received inside buildings, at subterranean locations, or underwater. Satellite communication and navigation systems have a variety of applications on land, at sea, and in the air. For example, satellite communication and navigation systems may facilitate activities such as banking, mobile phone operations, navigation of commercial aircraft and boats, scientific studies, tracking, and surveillance.
There is growing reliance of aircraft on satellite communication, navigation and information (e.g., weather) systems. Satellite signals may be spoofed to disrupt aircraft operations and/or to crash the aircraft. For example, a spoofed satellite navigation signal may attempt to cause an aircraft to fly off course. An ability to authenticate satellite signals protects against spoofing. Some techniques to authenticate satellite signals may rely on unique characteristics of the signals, and therefore cannot be applied to all satellite signals. For example, techniques used to authenticate a navigation signal may not work for a communication signal.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.